U.S. patent application number 12/653490 was filed with the patent office on 2010-07-08 for ammonia storage system.
Invention is credited to Lukas Burgi, Pascal Gerner, Mark Hornung, Felix Mayer.
Application Number | 20100172816 12/653490 |
Document ID | / |
Family ID | 40652720 |
Filed Date | 2010-07-08 |
United States Patent
Application |
20100172816 |
Kind Code |
A1 |
Mayer; Felix ; et
al. |
July 8, 2010 |
Ammonia storage system
Abstract
A system for storing ammonia comprises gas detector that is able
to detect gases other than ammonia. The system further comprises
thermally activatable ammonia stores, which can be activated to
release ammonia upon heating. When the ammonia stores are not
heated, the system is below ambient pressure and any leak will
cause external gas to enter the system. Therefore, the gas detector
is used to detect the presence of such external gas, which allows
to detect leaks. The gas detector may be embodied as a thermal
detector using a single heater and two temperature sensors for
detecting a gas flow as well as external gas.
Inventors: |
Mayer; Felix; (Stafa,
CH) ; Hornung; Mark; (Stafa, CH) ; Burgi;
Lukas; (Zurich, CH) ; Gerner; Pascal; (Zurich,
CH) |
Correspondence
Address: |
RICHARD F. JAWORSKI;Cooper & Dunham LLP
30 Rockefeller Plaza
New York
NY
10112
US
|
Family ID: |
40652720 |
Appl. No.: |
12/653490 |
Filed: |
December 15, 2009 |
Current U.S.
Class: |
423/352 ;
422/119 |
Current CPC
Class: |
F01N 2610/1406 20130101;
Y02T 10/24 20130101; F01N 2560/025 20130101; F01N 2610/14 20130101;
Y02T 10/12 20130101; F01N 3/2066 20130101; F01N 2560/023 20130101;
Y02A 50/2325 20180101; Y02A 50/20 20180101 |
Class at
Publication: |
423/352 ;
422/119 |
International
Class: |
C01C 1/00 20060101
C01C001/00; B01L 5/00 20060101 B01L005/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 2, 2009 |
EP |
09000024.1 |
Claims
1. An ammonia storage system comprising a thermally activatable
ammonia store, which, upon thermal activation, releases ammonia
into an ammonia containing section of said system, and a gas
detector adapted to detect a presence of a gas other than ammonia
in said ammonia containing section.
2. The ammonia storage system of claim 1 wherein said gas detector
is a thermal detector measuring a parameter depending on one of a
thermal conductivity and a heat capacity of gas in said ammonia
containing section.
3. The ammonia storage system of claim 2 comprising a flow detector
in a duct of said ammonia containing section for measuring a gas
flow in said duct.
4. The ammonia storage system of claim 3 comprising a thermal flow
detector comprising a heater, wherein said heater is common to said
flow detector and said gas detector.
5. The ammonia storage system of claim 4 comprising at least one
temperature sensor adapted to measure a temperature change induced
by said heater, wherein said temperature sensor is common to said
flow detector and said gas detector.
6. The ammonia storage system of claim 5 comprising at least a
first and a second temperature sensor located at different
positions in respect to said heater.
7. The ammonia storage system of claim 6 further comprising a
control unit designed for calculating said gas flow by using a
difference between signals from said first and said second
temperature sensor and designed for detecting the presence of a gas
other than ammonia from the signal of at least one of said
temperature sensors.
8. The ammonia storage system of claim 7 wherein said control unit
is designed for detecting the presence of a gas other than ammonia
by using a sum of signals from said first and said second
temperature sensor.
9. The ammonia storage system of claim 3 further comprising a valve
at a downstream location from said flow detector and a system
controller adapted to detect a leak downstream from said flow
detector by detecting a non-zero flow at said flow detector when
said valve is closed.
10. A method for operating the ammonia storage system of claim 1
wherein said gas detector is operated at least when said ammonia
store is not being activated in order to detect said gas other than
ammonia.
11. The method of claim 10 wherein a thermal flow detector in a
duct of said ammonia containing section is used for measuring an
ammonia flow in said duct as well as for detecting said gas other
than ammonia.
12. The method of claim 11 wherein said flow detector is used for
measuring a leak downstream from said flow detector by detecting a
non-zero flow or a downstream-upstream flow.
13. Use of the system of claim 1 as an ammonia source in a vehicle.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the priority of European Patent
Application 09000024.1, filed Jan. 2, 2009, the disclosure of which
is incorporated herein by reference in its entirety.
BACKGROUND OF THE INVENTION
[0002] The invention relates to an ammonia storage system
comprising a thermally activatable ammonia store as well as to a
method for operating such a system.
[0003] Ammonia storage systems are used in a wide area of
applications. However, one area of particular interest is the
storage of ammonia in vehicles run by diesel powered engines, where
the ammonia can be used in a Selective Catalytic Reduction (SCR)
process for the catalytic decomposition of NO.sub.x compounds.
[0004] A particularly advantageous class of ammonia storage systems
is based on thermally activatable ammonia stores where ammonia is
physically or chemically bound in a solid storage matrix. Heating
the matrix increases the vapour pressure of ammonia and allows to
release ammonia at well-defined and secure rates. Examples of such
systems are e.g. described in WO 2006/081824 and WO 2007/000170 by
Amminex A/S, Denmark.
[0005] However, for any type of ammonia storage system, there
should be leak detectors that-are able to detect leakage of ammonia
from the system. Such leak detectors can e.g. be formed by ammonia
detectors located outside the storage system.
SUMMARY OF THE INVENTION
[0006] The problem to be solved by the present invention is
therefore to provide an ammonia storage system with improved leak
detection.
[0007] This problem is solved by the system and method according to
the independent claims.
[0008] According to a first aspect of the invention, there is
provided a system comprising a gas detector adapted to detect the
presence of a gas other than ammonia in the ammonia containing
section of the system.
[0009] This concept is in contrast to leak detection systems where
ammonia detectors are placed outside the ammonia containing section
of the system, or where pressure detectors are provided within the
ammonia containing section of the system to detect leaks. The
present scheme relies on the fact that in systems with thermally
activatable ammonia stores the ammonia pressure can drop to a level
below ambient pressure when the system is in idle or inactive mode,
i.e. when the ammonia store is not being heated. In this case, a
leak in the system leads to outside gas entering the ammonia
containing section, which then can be detected by the gas detector
provided.
[0010] According to a second aspect of the present invention there
is provided a method in which the gas detector is operated at least
when the ammonia store is not being activated, i.e. not being
heated, in order to detect the presence of gas other than
ammonia.
[0011] The gas detector can advantageously be any detector that
allows to detect the presence of the "gas other than ammonia", with
this term specifying any gas likely to leak into the ammonia
containing section of the system, in particular nitrogen and/or
oxygen.
[0012] In a particularly advantageous embodiment the gas detector
is a thermal detector that measures a parameter depending on one of
the thermal conductivity and the heat capacity of the gas in the
ammonia containing section of the system. When an external gas
enters this section the thermal conductivity and the heat capacity
change which can be used to detect the presence of the external
gas.
[0013] The gas detector can advantageously be combined with a
thermal flow sensor. In particular, the two detectors can have a
common heater and/or common temperature sensors. Hence, a single
device, e.g. integrated on a single semiconductor chip, can be used
for both flow metering as well as leak detection.
[0014] A system according to an embodiment of the invention may
especially be suited for being used as an ammonia source in a
vehicle, but it is also suited for other applications.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] The invention will be better understood and objects other
than those set forth above will become apparent from the following
detailed description of advantageous embodiments of the present
invention. Such description makes reference to the annexed
drawings, wherein:
[0016] FIG. 1 shows a block diagram of an ammonia storage system
according to an embodiment of the present invention,
[0017] FIG. 2 shows a block diagram of a combined flow and gas
detector used in a system according to an embodiment of the present
invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0018] System Overview:
[0019] FIG. 1 shows an exemplary embodiment of a system according
to the invention. The system is a device for the storage and
controlled release of ammonia. It comprises at least one ammonia
store 1 containing a matrix storing ammonia. Ammonia from the
matrix can be released by heating the store by means of a heater
(not shown).
[0020] The stores 1 are part of an ammonia containing section 2 of
the system, which includes various ducts, valves and other elements
as required by the specific application.
[0021] In the embodiment of FIG. 1, a valve 3 is provided at the
outlet of the system. When valve 3 is opened, ammonia can flow out
of the system. In general, valve 3 is only opened when the stores 1
are activated, in which case the ammonia containing section 2 of
the system is under elevated pressure.
[0022] The system of FIG. 1 further comprises a combined flow and
gas detector 4 for measuring a gas flow as well as for detecting
gases other than ammonia in the ammonia containing section 2.
Advantageously, detector 4 is arranged at a duct leading to valve
3, with valve 3 being downstream from the detector, and with
"downstream" designating the direction of ammonia flow when ammonia
is leaving the system through valve 3.
[0023] The operation of the system is controlled by a system
controller 10 as shown.
[0024] The function of the system is, in short, as follows. In
regular operation, for releasing ammonia from the system, one or
several of the stores 1 are heated to build up ammonia pressure
inside ammonia containing section 2. Then, valve 3 is opened and
ammonia is released as required. If the system is required to
generate a variable ammonia flow, valve 3 can be a variable valve
or it can be operated in pulsed manner using a pulse width
modulation technique.
[0025] When ammonia is flowing through value 3, detector 4 can be
used for measuring its mass flow. The signal from detector 4 can
e.g. be used for monitoring the gas flow or for controlling the gas
flow in a closed control loop.
[0026] When no ammonia is required, the stores 1 are not heated and
valve 3 is closed. In that case, if the system contains no leaks,
the gas within ammonia containing section 2 will generally be pure
ammonia. Its pressure, however, may be well below ambient pressure,
e.g. 1 bar. If ammonia containing section 2 has a leak, external
(ambient) gas will therefore enter ammonia containing section 2.
Such external gas can be detected by detector 4. When detector 4
detects a gas other than ammonia, an alert can be issued or other
appropriate measures may be taken.
[0027] System controller 10 advantageously operates detector 4 to
detect external gas at least when the ammonia stores 1 are not
activated, but it may also operate detector 4 to detect external
gas when the system is operating because, neither at rest nor in
operation, detector 4 should be able to detect any external gas in
section 2.
[0028] Gas and Flow Detector 4:
[0029] As schematically illustrated in FIG. 1, gas and flow
detector 4 can e.g. comprise a semiconductor chip 5 with sensors
and electronics integrated thereon.
[0030] If, as it is the case in the advantageous embodiment of FIG.
1, detector 4 is a combined gas and flow detector, it may e.g. be
designed as shown in FIG. 2. It comprises a heater 6 symmetrically
arranged between two temperature sensors 7 and 8. The design of the
heater 6 and the temperature sensors 7, 8 can e.g. be as shown in
EP 1840535 or WO 01/98736, with heater 6 arranged on a membrane
suspended over an opening or recess in the semiconductor chip and
the temperature sensors 7, 8 being arranged downstream and upstream
of heater 6.
[0031] In operation, heater 6 is heated and creates an
inhomogeneous temperature distribution in its neighbourhood,
thereby changing the temperature at the location of the temperature
sensors 7, 8. A flow as indicated by arrow F of FIG. 2 will lead to
a decrease of the temperature at the location of upstream
temperature sensor 7 and to an increase (low flow) or decrease
(high flow) of the temperature at the location of downstream
temperature sensor 8.
[0032] As shown in FIG. 2, detector 4 further comprises a control
unit 9, which calculates the gas flow from the difference between
the signals from the temperature sensors 7, 8 as described in EP
1840535, US 2004/0099057 or WO 01/98736. Control unit 9 can e.g. be
integrated on the semiconductor chip of detector 4, but it may also
be an external device or it may be implemented as part of system
controller 10.
[0033] As mentioned, detector 4 not only measures the mass flow of
ammonia in the duct leading to valve 3, but it also can be used as
a detector for detecting the presence of a gas other than
ammonia.
[0034] For example, the method as described in US 2004/0099057 can
be used, where control unit 9 not only measures the difference of
the signals from the temperature sensors 7, 8, but also their sum,
which allows to determine the thermal conductivity of the gas
surrounding it. If the thermal conductivity is found to be
different from the thermal conductivity of pure ammonia, a foreign
gas must be present and an alert can be issued.
[0035] Sensor 4 can also be used by system controller 10 to detect
a leakage downstream from it, in particular a leakage in valve 3.
When valve 3 is closed, a leakage at this location leads to a gas
flow at detector 4. Such a non-zero gas flow can be detected by
detector 4. When detector 4 detects a non-zero gas flow when valve
3 is closed, an alert can be issued.
[0036] If the stores 1 are not heated and pressure inside ammonia
containing section 2 is below ambient pressure, a leak at the
location of valve 3 will lead to a gas flow at detector 4 from the
downstream side. Such an inverse downstream-upstream gas flow over
a sufficiently long period of time is also a typical indicator of a
system malfunction.
[0037] Detector 4 advantageously is made of materials that
withstand ammonia. In particular, a combined glass-plastics
housing, as shown in U.S. Pat. No. 6,920,786, can e.g. be used.
[0038] The plastics part of the housing is advantageously a
polyester, in particular PBT, or polyamide, but other materials can
be used as well, such as PTFE, PTCFE, PP, PS, ABS, PE, PVC.
[0039] Alternative Gas and Flow Detectors:
[0040] In the above embodiment, a combined flow and gas detector
was used.
[0041] In other words, the gas and flow detectors share their
heater as well as their temperature sensors. It must be noted,
though, that the two detectors can also use separate heaters and/or
temperature sensors. For example, a temperature sensor associated
with the gas detector does not necessarily have to be arranged
upstream or downstream of heater 6, but it could also e.g. be
arranged cross-stream (i.e. at right angles to the gas flow) from
heater 6.
[0042] Also, neither the flow detector nor the gas detector
requires two temperature sensors. A single temperature sensor may
suffice, and even the heater itself can be used as temperature
sensor
[0043] It must be noted that, albeit advantageous, the combination
of flow detector and gas detector in a single device is not a
required aspect of the invention. In particular, the gas detector
can e.g. be located at a distance from the flow sensor,
advantageously in a region where the ammonia is not flowing. It may
consist of a single heater and temperature sensor measuring the
thermal conductance between heater and temperature sensor which
depends on the gas composition.
[0044] Neither is the invention restricted to the use of thermal
gas detectors, i.e. of gas detectors measuring a parameter
depending on the thermal properties of the gas. Other types of gas
sensors can be used as well, such as one or more of [0045] infrared
sensors detecting gas-specific absorption properties in the
infrared spectral range, [0046] electrochemical sensors, [0047]
adsorptive or absorbtive sensors measuring the presence of foreign
gas adsorbed or absorbed in a matrix, e.g. due to a change of
dielectric properties of the matrix.
[0048] These types of sensors are known to the skilled person.
[0049] To improve leak monitoring, it is also possible to place
more than one gas detector into ammonia containing section 2 of the
system.
[0050] While there are shown and described presently preferred
embodiments it is to be understood that the invention is not
limited thereto but may otherwise be embodied and practiced within
the scope of the following claims.
* * * * *